1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic storage apparatus.
2. Description of the Related Art
Applications of the magnetic storage apparatus such as an HDD (Hard Disk Drive) are increasing, and importance of the magnetic storage apparatus is increasing. In addition, in the magnetic recording medium such as a magnetic disk, the recording density is increasing at a rate of over 50% per year, and this trend may be expected to continue in the future. With this trend of increasing recording density, magnetic heads and magnetic recording media suited for the high recording density are being developed.
The magnetic storage apparatus may be provided with the so-called perpendicular magnetic recording medium in which an axis of easy magnetization within a recording layer is mainly oriented in a perpendicular direction. In the perpendicular magnetic recording medium, the effects of demagnetization is small in a boundary region between recorded bits, and a sharp bit boundary may be formed, to thereby suppress increase of noise, even when the recording density is high. In addition, in the perpendicular magnetic recording medium, the decrease in the recording bit volume caused by the high recording density is small, and the thermal stability of written bits (or characteristic to withstand heat fluctuation) may be improved. The thermal stability of written bits may also be simply referred to as “thermal stability”.
In order to cope with the demands to further improve the high recording density of the magnetic recording medium, studies are being made to use a single-pole head having a desirable write performance with respect to the perpendicular recording layer. More particularly, a proposed magnetic recording medium is provided with a back layer made of a soft magnetic material between the perpendicular recording layer and a nonmagnetic substrate, in order to improve the input and output efficiency of magnetic flux between the single-pole magnetic head and the magnetic recording medium.
Further, in order to improve the recording and reproducing characteristic and the thermal stability of the perpendicular magnetic recording medium, a Japanese Laid-Open Patent Publication No. 2004-310910 proposes using an orientation control layer, forming a recording layer with a multi-layer structure, and making crystal particles of each of the magnetic layers of the recording layer have a continuous columnar crystal shape, so that the perpendicular orientation of the recording layer may be improved, for example.
For example, a Japanese Laid-Open Patent Publication No. 7-244831 proposes using Ru for the orientation control layer. In addition, because a dome-shaped projection is formed at a peak part of the columnar crystal of Ru, it is reported in a Japanese Laid-Open Patent Publication No. 2007-272990 that when crystal particles of the recording layer or the like are grown on the Ru dome-shaped projection and the isolation structure of the grown crystal particles is promoted to isolate the crystal particles, this has the effect of growing the magnetic particles in the columnar shape.
For example, a Japanese Laid-Open Patent Publication No. 2009-70444 proposes forming the perpendicular recording layer from an alloy having CoCrPt as its main component, in the perpendicular magnetic recording medium having the perpendicular recording medium formed on the substrate via a soft magnetic underlayer and a nonmagnetic intermediate layer.
For example, a Japanese Laid-Open Patent Publication No. 2004-310910 proposes forming the perpendicular recording layer by two or more magnetic layers, making at least one of the magnetic layers to include Co as its main component and to include Pt and an oxide, and making the other of the magnetic layers to include Co as its main component and to include Cr but no oxide, in order to improve the recording and reproducing characteristic and the thermal stability, and enable high-density information recording and reproduction.
However, in the conventional magnetic recording medium and the conventional magnetic storage apparatus, it may be difficult to improve the recording capacity.